<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>test</title>
</head>
<body>
    <div id="a"></div>
</body>
<script>
    function P(a){
        this.a = a;
        console.log(this.a);
        this.aaa = 134;
        console.log(this);
    }
    var a = document.getElementById("a");
    var s = new P(a);
    console.log(s);
</script>
</html>